The oil and gas industry makes wide use of coiled tubing, in for example well intervention, coiled tubing drilling and pipeline maintenance. In order to inject tubing into a well, and also pull it therefrom, a tubing injector must be provided on the surface. Conventional tubing injectors are large and heavy, and also relatively complex. The main reason for this is the very large pulling and injection forces required for the successful deployment of the tubing.
In order to repair sub-sea pipelines, coiled tubing can be injected through a hot tap while the pipeline is under a pressure of typically 100–200 bar. This tubing is used to deploy inflatable stoppers or plugs to isolate particular pipeline sections. By doing this, repairs can be made to the isolated sections without having to close down the entire pipeline, which as will be appreciated would incur considerable costs and cause considerable inconvenience.
A problem with existing injectors is that injection and indeed ejection of coiled tubing can be difficult to control when there is a pressure differential between the pipeline and the exterior of the tool. Typically, large injection and pulling forces are needed, which as noted above, means that equipment tends to be large and heavy. This can cause problems, because pipeline repairs often need to be done at short notice, anywhere in the world and deployed from a variety of support vessels. The need for rapid deployment means that it is important that tubing injectors are compact and can be easily broken down into small parts for transportation by conventional aircraft and/or helicopter. In addition, the injectors have to be simple enough to be reliable and easily stripped down and serviced in the field.
An object of at least one embodiment of the invention is to provide a simple and compact coiled tubing injector.